Preparation and tribological behavior of Cu-nanoparticle polyelectrolyte multilayers obtained by spin-assisted layer-by-layer assembly

Polyelectrolyte multilayers (PEMs) fabricated by spin-assisted layer-by-layer assembly technique were used as nanoreactors for in-situ synthesis Cu nanoparticles. Chemical reaction within the PEMs was initiated by a reaction cycle in which Cu²⁺ was absorbed into the polymer-coated substrate and then reduced in NaBH₄ solutions. Repeating the above process resulted in an increase in density of the nanoparticles and further growth in the dimension of the particles initially formed. So, different Cu-nanoparticle polyelectrolyte multilayers were formed in the process. The friction and wear properties of Cu-nanoparticle PEMs formed by different reaction cycles were investigated on a microtribometer against a stainless steel ball. The PEMs reinforced with Cu nanoparticles, prepared under the best preparation conditions, possess good tribological behavior, because of the weakened adhesion between the PEMs and the substrate and decreased mobility of the polymeric chains in the presence of excessive Cu nanoparticles generated at larger reaction cycles.     

Spray-Assisted Polyelectrolyte Multilayer Buildup: from Step-by-Step to Single-Step Polyelectrolyte Film Constructions

The alternate deposition of polyanions and polycations on a solid substrate leads to the formation of nanometer to micrometer films called Polyelectrolyte Multilayers. This step-by-step construction of organic films constitutes a method of choice to functionalize surfaces with applications ranging from optical to bioactive coatings. The method was originally developed by dipping the substrate in the different polyelectrolyte solutions. Recent advances show that spraying the polyelectrolyte solutions onto the substrate represents an appealing alternative to dipping because it is much faster and easier to adapt at an industrial level. Multilayer deposition by spraying is thus greatly gaining in interest. Here we review the current literature on this deposition method. After a brief history of polyelectrolyte multilayers to place the spraying method in its context, we review the fundamental issues that have been addresses so far. We then give an overview the different fields where the method has been applied.     

Paradigm shift from self-assembly to commanded assembly of functional materials: recent examples in porphyrin/fullerene supramolecular systems

Abstract

Current nanotechnology based on top-down nanofabrication may encounter a variety of drawbacks in the near future so that development of alternative methods, including the so-called bottom-up approach, has attracted considerable attention. However, the bottom-up strategy, which often relies on spontaneous self-assembly, might be inefficient in the development of the requisite functional materials and systems. Therefore, assembly processes controlled by external stimuli might be a plausible strategy for the development of bottom-up nanotechnology. In this review, we demonstrate a paradigm shift from self-assembly to commanded assembly by describing several examples of assemblies of typical functional molecules, i.e. porphyrins and fullerenes. In the first section, we describe recent progress in the design and study of self-assembled and co-assembled supramolecular architectures of porphyrins and fullerenes. Then, we show examples of assembly induced by external stimuli. We emphasize the paradigm shift from self-assembly to commanded assembly by describing the recently developed electrochemical-coupling layer-by-layer (ECC-LbL) methodology.     

功能性层层组装厚膜

层层组装是一种基于物质交替沉积而制备复合膜的方法,可以实现膜的结构和组成的精确调控。层层组装通常被认为是超薄膜的构筑方法。与超薄膜相比,微米或亚微米的厚膜更容易实现高的负载、微纳复合结构的调控、多功能集成以及赋予膜更高的稳定性。以作者的研究结果为基础,阐明TN用大尺度的构筑基元,包括聚合物复合物、大尺度的无机粒子以及聚集的粒子,可以方便地实现微米厚度的层层组装膜的快速构筑。以快速构筑的厚膜为功能载体,实现了层层组装膜的自修复、高负载、细胞可控粘附及多功能集成。进一步,将层层组装厚膜从基底上剥离制备了自支持膜,拓展了层层组装膜的功能。     

[(PMo12O403-)/PAMAM-Cu2+]n多层膜的制备和电化学行为

采用层层自组装的方法,把多金属氧酸盐PMo12O403-和与Cu2+络合的聚酰胺-胺树形分子PAMAM(PAMAM-Cu2+)交替吸附成膜。X射线光电子能谱(XPS)、紫外可见光谱(UV-Vis)、原子力显微镜(AFM)和循环伏安法(CV)测试表明,PMo12O403-和PAMAM-Cu2+能通过静电作用形成多层膜且膜的增长均一稳定,该多层膜修饰电极对H2O2和NO2-有较好的电催化还原活性。     

A silver nanoparticle thin film modified glass substrate as a colourimetric sensor for hydrogen peroxide

In this work, a silver nanoparticle (AgNP) coated glass slide was developed as a device for sensing hydrogen peroxide. AgNPs were synthesised using borohydride reduction with a citrate stabiliser, resulting in a negatively charged stabilised particle surface. The particles were attached to the glass surface using the layer-by-layer (LbL) technique. Poly (diallyldimethylammonium chloride) and poly (styrene sulphonate) were used as cationic and anionic polyelectrolyte layers, respectively. The glass slide was modified with polyelectrolytes leaving a cationic layer on the top surface. The AgNPs were subsequently deposited on the slide via electrostatic interaction. As a result, a dark yellow film of AgNPs was obtained with maximum absorption at 410 nm. Film fabrication based on LbL assembly provided acceptable reproducibility (relative standard deviation = 6.5%). The fabricated film had long-term stability (>6 weeks). A very small quantity of AgNPs was used in this method. Fabrication was performed under ambient conditions. Therefore this fabrication was considered as a green method. The AgNP modified slide was developed to sense hydrogen peroxide. Detection is based upon oxidation of AgNPs by hydrogen peroxide. This results in a change in colour of the film from dark yellow to colourless. Linear calibration was obtained over the range of 1.0--100.0 mM of hydrogen peroxide. The device was successfully used for measuring hydrogen peroxide in urine.     

Preparation of Phospholipid Multilayer Patterns of Controlled Size and Thickness by Capillary Assembly on a Microstructured Substrate

By dragging a phospholipid solution on microstructured silicon surfaces, phospholipid molecules are selectively deposited inside the microstructures to get regular phospholipid multilayer patterns of controlled thickness over a large scale (～cm²). By varying the dragging speed, the thickness of the patterns varies between 28 and 100 nm on average (7 to 25 bilayers). Electroswelling of phospholipid multilayer patterns leads to the formation of giant liposomes of controlled size and narrow size distributions.     

Polysaccharide‐Blend Multilayers Containing Hyaluronan and Heparin as a Delivery System for rhBMP‐2

It is shown that blend multilayers of hyaluronan (HA) and heparin (HEP) as polyanions and poly(L‐lysine) (PLL) as a polycation can be used to prepare films with different thicknesses and chemical compositions. The amounts of recombinant human BMP‐2 (rhBMP‐2) loaded and the fraction initially released from the films depend on the film's chemical composition. The amounts of rhBMP‐2 loaded in the films are much higher for HA mass fractions of more than 0.4. The bioactivity of the rhBMP‐2‐loaded films is investigated on C2C12 myoblasts, which differentiates into osteoblasts in contact with the films. The alkaline phosphatase expression for cells grown on nanoblend films of various compositions falls over a unique curve. This suggests that the cells “sensing” the rhBMP‐2 are not influenced by the film's chemistry. The rhBMP‐2 can sustain at least three successive culture sequences while remaining bioactive, thus confirming the important and protective effect of rhBMP‐2. Altogether, these results indicate that crosslinked PLL/HA films have superior properties for the incorporation of rhBMP‐2 and on its long‐lasting bioactivity.     

Green nanochemistry: metal oxide nanoparticles and porous thin films from bare metal powders

A universal, simple, robust, widely applicable and cost-effective aqueous process is described for a controlled oxidative dissolution process of micrometer-sized metal powders to form high-purity aqueous dispersions of colloidally stable 3-8 nm metal oxide nanoparticles. Their utilization for making single and multilayer optically transparent high-surface-area nanoporous films is demonstrated. This facile synthesis is anticipated to find numerous applications in materials science, engineering, and nanomedicine.     

基于层层组装法构建阻燃天然纤维素纤维织物的研究进展

利用层层组装(LBL)法构建阻燃天然纤维素纤维织物是基于相反电荷聚电解质的物理吸附作用,在织物表面交替沉积而成多层膜的一种新型阻燃改性方法。与传统方法相比,LBL法可以在基体与外部环境之间构建阻燃多层膜,从而直接干扰燃烧过程;尤其是通过对组装条件和过程的调节,可以方便地控制多层膜的质量、厚度和元素组成,进而对阻燃性能进行有效调控。总结了近年来国内外基于LBL法构建纳米材料-纳米材料、纳米材料-聚电解质及聚电解质-聚电解质阻燃天然纤维素纤维织物的研究进展,介绍了本课题组在苎麻织物表面构建氨基化碳纳米管-聚磷酸铵和聚乙烯亚胺-聚磷酸铵膨胀型阻燃涂层方面所做的探索性工作,展望了其未来的发展趋势。     

Surface functionalization of nanoparticles to control cell interactions and drug release

Nanoparticles made from poly(dl-lactide-co-glycolide) (PLGA) are used to deliver a wide range of bioactive molecules, due to their biocompatibility and biodegradability. This study investigates the surface modification of PLGA nanoparticles via the layer-by-layer (LbL) deposition of polyelectrolytes, and the effects of these coatings on the release behavior, cytotoxicity, hemolytic activity, and cellular uptake efficiency. PLGA nanoparticles are modified via LbL adsorption of two polyelectrolyte pairs: 1) poly(allylamine hydrochloride) (PAH) and poly(styrene sulfonate) (PSS) and 2) poly(L-lysine hydrobromide) (PLL) and dextran sulfate (DES). It is demonstrated that both PAH/PSS and PLL/DES coatings suppress the burst release usually observed for unmodified PLGA nanoparticles and that the release behavior can be adjusted by changing the layer numbers, layer materials, or by crosslinking the layer constituents. Neither bare nor polyelectrolyte-modified PLGA nanoparticles show any signs of cytotoxicity. However, nanoparticles with a positively charged polyelectrolyte as the outermost layer induce hemolysis, whereas uncoated particles or particles with a negatively charged polyelectrolyte as the outermost layer show no hemolytic activity. Furthermore, particles with either PAH or PLL as the outermost layer also demonstrate a higher uptake efficiency by L929 fibroblast cells, due to a higher cell-particle affinity. This study suggests that LbL coating of PLGA nanoparticles can control the release behavior of bioactive molecules as well as the surface activity, therefore providing a promising strategy to enhance the efficiency of nanoparticulate drug-delivery systems.